1. Field of the Invention
The present invention relates to head cartridges ejecting predetermined liquid from liquid-ejecting nozzles formed in the liquid-ejecting heads to targets and to liquid-ejecting apparatuses including the same.
2. Description of the Related Art
Known liquid-ejecting apparatuses such as ink-jet printers print by energizing ejection-driving means such as heating elements and piezoelectric elements disposed in liquid chambers in printheads, and by ejecting drops of predetermined liquid, i.e. ink, in the liquid chambers from ink-ejecting nozzles to recording paper so that the ink drops adhere thereto. Due to advantages such as low unit prices, low running costs, high resolution, and compact bodies, liquid-ejecting apparatuses are in widespread use.
Inside the body, each of the ink-jet printers includes a detachable head cartridge composed of a printhead ejecting ink from ink-ejecting nozzles that are formed in a nozzle plate of the printhead, an ink tank containing the ink that is to be supplied to a liquid chamber in the printhead, an ink-supplying conduit supplying the ink from the ink tank to the printhead, an ink-refluxing conduit refluxing the ink from the printhead to the ink tank, and a liquid-delivering pump for circulating the ink between the printhead and the ink tank.
Such a head cartridge needs to stably eject ink drops in the order of, for example, picoliters from the ink-ejecting nozzles, however, the microscopic ink-ejecting nozzles occasionally cause ink-ejecting failure and impair print quality due to various factors.
One of the factors is bubbles trapped in the printhead and the periphery. When trapped in the ink-supplying conduit or the liquid chamber, the bubbles hinder the stable ink ejection from the ink-ejecting nozzles, and, furthermore, may cause printing failure due to ink nonejection.
Possible sources of the bubbles trapped in the printhead and the periphery include air entering a socket of the ink tank when the ink tank detachable from the printhead is replaced, separation of air that is dissolved in the ink due to changes in temperature or pressure, air entering from the ink-ejecting nozzles due to vibration or impacts during printing or during a halt in printing, air penetrating from conduit members composing ink channels between the ink tank and the printhead, and the like.
These bubbles trapped in the printhead are removed by circulating the ink between the ink tank and the printhead. For example, Japanese Patent No. 2733277 (Page 3, FIG. 16) discloses a technique for ink circulation in which a secondary ink tank is disposed between a main ink tank and a printhead, and a recovery pump delivers ink from the secondary ink tank to the printhead.
Furthermore, Japanese Unexamined Patent Application Publication No. 10-138515 (Page 4, FIG. 1) discloses a technique in which a circulation pump is disposed on an ink-supplying channel extending from an ink tank so as to circulate ink in the ink-supplying channel and in a liquid chamber in a printhead between the ink tank and the printhead, and a head cap that can seal a nozzle plate of the printhead comes into contact with the nozzle plate so as to suck the ink by reducing the pressure inside the head cap.
However, in each of these known techniques, the ink circulates due to a positive pressure applied to the printhead by the pump, and this structure sometimes causes ink leakage from the ink-ejecting nozzles of the printhead during the ink circulation. The leaked ink can contaminate the periphery of the nozzles. Moreover, for a full-line printhead having a large number of nozzles in the nozzle plate over the width of, for example, A4 recording paper, a large volume of the ink leaked from the ink-ejecting nozzles is wasted.
Furthermore, these techniques need solutions for the ink leakage from the ink-ejecting nozzles during the ink circulation. In Japanese Patent No. 2733277, an ink absorbent absorbs the leaked ink. In Japanese Unexamined Patent Application Publication No. 10-138515, the head cap that is brought into contact with the nozzle plate of the printhead sucks the leaked ink. To cope with these solutions, an ink-circulation system to recycle the leaked ink may be employed, however, this may cause upsizing of the apparatuses and an increase in cost.